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Characterization of msim, a murine homologue of the Drosophila sim transcription factor
1Department of Biochemistry, McGill University, 3655 Drummond Street, Montreal, Quebec, H3G 1Y6, Canada.
Abstract:
Mutations in the Drosophila single-minded (sim) gene result in loss of precursor cells that give rise to midline cells of the embryonic central nervous system. During the course of an exon-trapping strategy aimed at identifying transcripts that contribute to the etiology and pathophysiology of Down syndrome, we identified a human exon from the Down syndrome critical region showing significant homology to the Drosophila sim gene. Using a cross-hybridization approach, we have isolated a murine homolog of the Drosophila sim gene, which we designated msim. Nucleotide and predicted amino acid sequence analyses of msim cDNA clones indicate that this gene encodes a member of the basic-helix-loop-helix class of transcription factors. The murine and Drosophila proteins share 88% residues within the basic-helix-loop-helix domain, with an overall homology of 92%. In addition, the N-terminal domain of MSIM contains two PAS dimerization motifs also featured in the Drosophila sim gene product, as well as a small number of other transcription factors. Northern blot analysis of adult murine tissues revealed that the msim gene produces a single mRNA species of approximately 4 kb expressed in a small number of tissues, with the highest levels in the kidneys and lower levels present in skeletal muscle, lung, testis, brain, and heart. In situ hybridization experiments demonstrate that msim is also expressed in early fetal development in the central nervous system and in cartilage primordia. The characteristics of the msim gene are consistent with its putative function as a transcriptional regulator.
Insights
Researchers identified a mouse gene, msim, homologous to Drosophila sim, which is crucial for embryonic central nervous system development. This transcription factor may play a role in mammalian development and disease.
Area of Science:
- Developmental Biology
- Genetics
- Molecular Biology
Background:
- Mutations in Drosophila single-minded (sim) disrupt embryonic central nervous system midline cell development.
- A human exon homologous to Drosophila sim was identified within the Down syndrome critical region.
Purpose of the Study:
- To identify and characterize a murine homolog of the Drosophila sim gene.
- To investigate the potential role of this gene in mammalian development.
Main Methods:
- Cross-hybridization to isolate the murine homolog (msim).
- Nucleotide and amino acid sequence analysis of msim cDNA.
- Northern blot and in situ hybridization for expression analysis.
Main Results:
- A murine homolog, msim, was isolated and found to encode a basic-helix-loop-helix transcription factor.
- MSIM shares high homology with Drosophila SIM, including conserved functional domains (basic-helix-loop-helix, PAS motifs).
- msim exhibits specific expression patterns in adult tissues and during fetal development, notably in the central nervous system and cartilage.
Conclusions:
- The msim gene is a functional homolog of Drosophila sim.
- Its conserved structure and expression patterns suggest a role as a transcriptional regulator in mammalian development, potentially relevant to Down syndrome pathophysiology.